The repair of thin film wiring using TSM repair lines is well known. In the conventional repair process, a defective electrical wiring net, used to connect components on a circuit board, is disconnected from its internal wiring through specialized delete locations located at the "C4" joining pads. ("C4" means the Controlled-Collapsed-Chip-Connection technique used to connect semiconductor chips to the holes or vias between layers of a circuit board.) The net is reconstructed with equivalent electrical performance by connecting the X-Y grid of the repair lines on the top surface to the required C4 pads, matching the timing of the original net.
The reconstruction of the net is normally accomplished by joining the segments of the repair lines with individual gold slugs bonded to the TSM repair lines through a lasersonic bonding methodology. The gold slugs interconnect specific X and Y repair line segments to rebuild the net topography.
FIG. 1 illustrates a portion of a conventional multi-chip module (MCM) before repair. In FIG. 1, C4 connection 10 is connected to net 12 at via 14. X repair line 16 and Y repair lines 18, 20 are part of the top layer. Y repair lines 18, 20 are connected by Y repair line subway 22 using vias 24, 26. Vias 14, 24, 26 connect to down levels. C4 connection 10 has a repair elbow 28 and a bond site 30.
The reconstruction of the net during a conventional repair process is normally accomplished by joining the segments of the repair lines with individual gold slugs bonded to the TSM of the repair through conventional lasersonic bonding processes. The gold slugs interconnect specific X and Y repair line segments to rebuild the net topography. FIG. 2 is a plan view of the portion of the device shown in FIG. 1 after the conventional repair process. (FIG. 3 is a cross-sectional view taken along the line 3--3 of FIG. 2.) When a short is found in net 12, it is completely disconnected from the circuit using external delete 32 between C4 connection 10 and via 14. This process is repeated at every other C4 connection location for net 12. To replace this deleted net, a portion of X repair line 16 and Y repair lines 18, 20 must be used. Conventionally, X repair line 16 and Y repair lines 18, 20 are cut using deletes. Then C4 connection 10 is connected to X repair line 16 using gold slug 34, and X repair line 16 is connected to Y repair line 20 using gold slug 36.
One drawback of the conventional repair process illustrated in FIGS. 1-3 is that a relatively large number of repair lines are consumed for nets with multiple segments. As illustrated in FIG. 2, an X repair line and a Y repair line were necessary to replace net 12. This results in fewer nets being repairable. This drawback is illustrated in FIG. 4, which shows two nets. C4 connection 10 (a signal connection) is part of net 12; C4 connection 40 (also a signal connection) is part of the second net 42. Power-ground C4's 44, 46 are also shown. Because most defective nets run in the same general direction on the device, they require the use of the same top-surface repair lines. In such a case a part might be lost due to "unroutability," defined as insufficient repair lines to meet the repair requirements. Only one of the two nets illustrated in FIG. 4 can be repaired using the conventional process because both need access to X repair line 16.
The conventional gold lasersonic bonding technique works well for planarized thin film structures. In the new generation of multilayer thin film products using "CMOS" or Complementary Metal-Oxide-Semiconductor systems, however, the thin film structures are not planarized. The surface topography caused by the non-planarized films significantly reduces the effectiveness of the lasersonic bonding technique. This reduced effectiveness increases the risk of reliability defects associated with the bonds and reduces the yield of substrates which require a large number of bonds. This problem has effectively limited the number of defects that may be repaired and creates unnecessary yield loss. On some products, the yield loss may be as high as fifteen percent.
In view of the shortcomings of the prior art, a new process and system are needed to improve the repair process of thin film products. One approach, titled "Method for Repairing Defective Electrical Connections on Multi-Layer Thin Film (MLTF) Electronic Packages and the Resulting MLTF Structure," is the subject of U.S. patent application Ser. No. 08/577,677, filed on Dec. 21, 1995. Provided below is another approach.